Lubricating oil additives



VISCOSITY 4D IOOF. (S.U.S.) AFTER HEATING IN AIR AT 350 FOR 24 HRS.

April 13, 1948.

SIG

c. M. HIMEL El AL 2,439,734

I LUBRICATING OIL ADDI'I'IVES Filed Feb. 11, 1946 n N, N DIAMYL a BUTYL SULF'ENAMIDE o =N-t=- BUTYLSULFENYLMORPHOLNE x=N-t- BUTYLSULFENYLPJPERIDINE 0.2 0.4 0.6 0.8 I. I2 1.4 L6 L8 2.0

WT. Z, INHIBITOR m LUBRICATING QIL INVENTORS C.M.HIMEL G.C.BA|LEY BY Maia ATTORNEYS Patented Apr. 13, 1948 LUQBICATIN G OIL ADDITIVES Chester M. Himel and Grant C. Bailey, Bartlesville, kla., assignors to Phillips Petroleum Company, a corporation of Delaware Application February 11, 1946, Serial No. 646,734

12 Claims. (Cl. 252-47) This invention relates to lubricating oil additives which are particularly valuable in increasing the resistance of said oils toward oxidation. More specifically the invention relates to the use of sulfenamides as antioxidants for lubricating oils. The invention is further concerned with a method for inhibiting the oxidation of lubricating oils through the use of a class of compounds known as alkyl sulfenamides which may be synthesized by the interaction of aliphatic mercaptans with primary and secondary amines.

There are numerous factors involved in the deterioration of a lubricating oil. On account of the complex nature of lubricating oils and the .variety of uses to which they are subjected, many problems arise which must be solved if these materials are to be satisfactory. One of the principal factors involved in the deterioration of an oil is the reaction with oxygen. I It is obvious that any addition agent which will retard the rate of oxidation of a lubricating oil is highly desiraable. Some agents of this type, however, may also influence the direction and character of other accompanying reactions such as polymerization, condensation and the like, with the result that many of the oxidation products may be affected. It is, therefore, important that any additive which is employed to reduce or substantially eliminate oxidation of the oil must not induce other reactions which will produce undesirable effects.

The principal object of the present invention is to provide improved lubricating oil additives and lubricating oil containing the same. Another object is to provide additives which increase the resistanceof lubricating oils toward oxidation.

Another object is to provide additives which give superior protection against oxidation at a very low cost per unit of finished oil. Another object is to provide additives which are unobjectionable both initially and upon. prolonged use of the oil in an engine. Another object is to provide additives which can be made at low cost from relatively cheap and readily available raw materials. Many other objects will more fully hereinafter appear.

We have now found that alkyl sulfenamides have superior properties as lubricating oil additives and are particularly effective as antioxidants. These compounds when added in relatively small quantities to lubricating oils, exert an unexpected reduction in the tendency of the oils to oxidize and, at the same time, do not produce deleterious effects on other properties.

The alkyl sulfenamides employed in carrying out this invention comprise a group of compounds containing the linkage and may be represented by the formula wherein R1 is an alkyl group, either unsubstituted or substituted, and R: and R3 are hydrogen or substituted or unsubstituted alkyl, aralkyl, aromatic or cycloalkyl groups and wherein R2 and R3 may be the same or different and wherein R2 and R1 may be part of a cyclic structure, for example, may have a bond directly connecting them or other linkage such that with the nitrogen atom a heterocyclic ring, usually six-m'embered, is formed. R1, R2 and R3 may be the same alkyl groups or may consist of any combination of the indicated groups.

Upon heating in the presence of oxygen, most uninhibited oils show marked increases in the values for neutralization number, carbon residue and viscosity. All three of these values may be considered as indications of the stability of a given oil toward oxidation. The eifectiveness of an oxidation inhibitor may be measured by its ability to minimize the increases in these values which would normally occur upon heating. In general there is a direct correlation between antioxidant effect and the values for neutraliza: tion number, carbon residue and viscosity. In most oils an increase in viscosity occurs on heating in air and an antioxidant prevents this increase. The particular oils tested to obtain the data reported herein displayed this characteristic.

The oxidation stability of both the uninhibited and the inhibited oils was determined by the aluminum block method as follows. The apparatus consists essentially of an electrically heated and thermally insulated block of aluminum which has been bored out to receive beakers of about 400 ml. capacity in which the oil is heated. The temperature of the block is thermostatically controlled to give the desired oil temperature in the beakers. Samples of oil are heated in contact with air at a temperature of 350 F. for twentyfour hours and the changes in physical charac-- Oils. It is a well-known and accepted method for determining lubricating oil stability.

Our invention is generally applied to mineral lubricating oils, that is oils of petroleum or hydrocarbon origin. However, it is equally applicable to mixtures of mineral lubricating oil and other oils such as oils of animal or vegetable origin. Application of our invention to nonmineral lubricating oils is not excluded. Likewise the invention is not limited to oils used for lubricating internal combustion engines, but may be applied to oils used for any lubricating service where resistance to oxidation is desired.

The synthesis of the compounds employed in accordance with the present invention may be effected by various means. In a copending application of one of us, Serial No. 617,871, flied September 21, 1945, a method for the preparation of alkyl sulfenamides from alkyl mercaptans and amines is described. The synthesis may be accomplished with both primary and secondary allphatic or aromatic amines as well as with heterov cyclic amines which are secondary such as morpholine, thiomorpholine, piperidine, etc. When cyclic amines such as morpholine are employed. the nitrogen atom in the resulting sulfenamide is a part of the morpholine ring.

For a detailed description of one method of making the sulfenamides used in practicing the present invention, attention is directed to said application Serial No. 617,871. which is hereby incorporated herein by reference. However it is to be understood that any other method of preparation of the sulfenamides which may be discovered in the future may be employed and that the present invention is not concerned with the preparation of the compounds but with their utilization as improved oil additives.

.In practicing our invention we take lubricating oil of any suitable type and blend therewith in any suitable manner a minor proportion of the alkyl sulfenamide. The addition is usually accomplished by simple admixtures since the additives of the present invention are readily soluble in lubricating oil to an extent much more than suflicient to effect substantially complete inhibition of oxidation of the oil.

The amount of the alkyl sulfenamide employed will almost invariably be less than 8 per cent by weight based on the weight of the oil. Generally it will range between 0.01 and 5 per cent by weight. We have found that there is for every specific alkyl sulfenamide an upper limit beyond which increased amounts of the compound exert no additional antitoxidant eilect. This is illustrated in the accompanying drawing in which viscosity measured in Saybolt Universal seconds at 100 F. after heating in contact with air at a temperature of 350 F. for twenty-four hours is plotted against per cent by weight of three different alkyl sulfenamides used as-antioxidants in accordance with this invention. The allwl sulfenamides shown are N,N-diamyl-t-butyl sulfenamide, N-t-butylsulfenylmorpholine and N- t-butylsulfenylpiperidine. The oil used was a Mid-Continent neutral oil having a viscosity of approximately 290 Saybolt Universal seconds at 100 F. before heating. It will be observed that increases in amount of the sulfenamides above 1, 0.25 and 0.1 per cent, respectively for the three named sulfenamides. gave no further reduction in viscosity increase. However we often prefer to use amounts somewhat in excess of these critical amounts in order to provide a reserve of antioxidant in the oil during the life of the oil to take care of possible loss by volatilization and decomposition especially while in the engine. The excess amount may vary from 20 to 300 per cent of the critical amount. An even greater excess may be employed. For example in the case of inhibitors such as the tertiary butyl sulfenamides of morpholine and piperldine of which only a few tenths of one per cent produce maximum inhibition, we may employ amounts ranging as high as 1 per cent or even 2 per cent.

Our invention is based on the discovery that the alkyl sulfenamides have the unique combination of properties which render them outstandingly valuable as lubricating oil antioxidants. They have the requisite degree of stability and anti-oxidant power as well as compatibility with a wide range of lubricating oils. They may be made from cheap and available raw materials such as petroleum mercaptans.

Examples of alkyl groups which may be attached to the sulfur atom are methyl, ethyl, n-propyl, isopropyl, and higher ranging as h h as C20 or even higher. Alkyl groups having 4 or more carbon atoms are preferred because they impart lower volatility to the resulting sulfenamide. Tertiary alkyl groups are preferred because of the greater availability and lower cost of tertiary mercaptans and the greater ease ofpreparation of the tertiary alkyl sulfenamides. Tertiary butyl and tertiary heptyl are examples of tertiary alkyl groups which are eminently satisfactory.

The alkyl group connected to sulfur in the sulfenamide is ordinarily unsubstituted. However it may be substituted. Examples of substituents which may be present on the alkyl group are halogens, namely fluorine, chlorine, bromine and iodine, nitro groups, suflde groups (-SR), etc.

The amines employed in the preparation of the sulfenamides used in the present invention are preferably high-boiling, i. e. have a low vapor pressure, in order to produce an additive of low volatility so that it remains in the oil upon use. Other than this factor a very wide range of amines can be used to give inhibitors of varying anti-oxidant power. For instance, excellent results'have been obtained with the sulfenamides prepared from tertiary butyl mercaptan and the following amines: diamylamine, morpholine and piperidine. In the case of these three amines the corresponding tertiary butyl sulfenamides gave essentially complete inhibition of oxidation of a selected Mid-Continent lubricating oil base, using concentrations of 1, 0.25 and 0.1 per cent respectively, as is illustrated in the accompanying drawing. Other amines which are useful include aniline, N-methyl aniline, N-ethyl aniline, N-

amine, dimethylamine, di-n-butylamine, piperazine, thiomorpholine, or any other primary or secondary amine including ammonia.

By using a higher-boiling mercaptan, such as tertiary amyl, tertiary hexyl, or tertiary heptyl, sulfenamides of lower volatility are produced. Similarly by using a higher-boiling amine, a decrease in volatility of the sulfenamide is attained. It is often preferred either to use a mercaptan containing more than 4 carbon atoms per molecule or to use an amine having a boiling point above C., or to use both of these expedients if desired, to reduce evaporation losses during use of the lubricating oil prepared in accordance with the present invention. It will be understood that by using a higher mercaptan it is in general possible to use a lower-boiling amine and vice versa, in order to obtain sulfen'amides of like volatility.

The sulfenamide made from tertiary butyl mercaptan and piperidine was the most effective antioxidant of those tested. This compound has the formula Ha Hs c-c t-can-a-n on,

(2-0 Rs Hg and may be designated N-t-butylsulfenylpiperidine.

Next in effectiveness was the sulfenamide made from tertiary butyl mercaptan and-morpholine, denoted N-t-butylsulfenylmorpholine and having the formula Ha Ha Two antioxidants which are especially valuable for practicing the present invention, particularly in view of their low volatility. are the tertiary butyl sulfenamides prepared from N-methyl aniline and from phenyl beta-naphthylamine. These are designated N-phenyl-N-methy1-t-butyl sulfenamide and N-phenyl-N-fimaphthyl-t-butyl sulfenamide, respectively.

Most of the alkyl sulfenamides which we have prepared are normally liquid materials or lowmelting solids and possess the advantageous property of relatively high solubility in mineral lue bricating oil,

Any lubricating oil may be used in practicing the invention. While we have made particular reference herein to a mineral oil of Mid-Continent origin, oils or blends of oils from any source may be used so long as they have lubricat ing properties. While the resulting product is usually used as a lubricating oil, it is to be understood that it may be put to other uses where resistance to oxidation of the lubricating oil is desired. For example it may be employed in the manufacture of greases. The employment in the lubricating oil of other additives and materials compatible with the. additives oi the present invention is within the scope of our invention.

, EXAMPLE I A sample of a sulfenamide prepared from morpholine and tertiary butyl mercaptan was tested to determine its value as a lubricating oil antioxidant. The sulfenamide was mixed with a neutral oil and the blend heated by the aluminum block method after which certain properties or the resulting material were studied. In order to determine the effect of the additive, a control test was made on a sample of oil in which none of the sulfenamide had been introduced. Table I shows the effect of heating a neutral oilwhile Table II gives the results obtained by heating that same oil to which 0.25 weight per cent of the sulfenamide had been added.

Tssu: I Eflect of heating on Mid-Continent neutral oil Tsau: II

Eflect of heating on Mid-Continent neutral oil containing 0.25 weight per cent N-t-but1!lsulfenu'lmorpholine New on Home?! Evagoration Loss 3. 7 Nap tha Insoluble, r cent--. 0. 03 Neutralization Num r 0.00 0.18 Carbon Residue, Rsmsbottom. 0.06 0.06 Viscosity at 100 F., SUB 287.3 311.4 Viscosity (corrected for Evaporation Loss). 308.9 Viscosity Increase, per cent 0. 81

EXAMPLE II Three parallel tests were made on a sample of oil to determine the efl'ect of the presence of an alkyl sulfenamide-on the oxidizing properties of the oil. The suli'enamide employed was that synthesized from tertiary butyl' mercaptan and morpholine. The procedure of Example I was followed. Table III gives the data obtained on I a sample of the neutral 011 without the additive and also shows the results of introducing the sulfenamide in amounts of 0.05 and 1.0 weight per cent, respectively.

TABLE HI Eifect of N-t-butyliiulj'enylmorphioli'ne on oxidizing properties of Mid-Continent neutral oil Oil-+0.05 0il+1.0 .Control per cent per cent Sulfenamide Sulienamide New Bagged Nqw Heated Ne-w Heated Oil 350 F 01] 011 R Evagoration Loss 4.2 3.8 3.9- Nap the Insoluble, per cant.. 0.08 0.07 0.04

Neutralization Number 0.07 0.47 0.06 0.33 0.06 0.03 Carbon Residue, Y

Ramsbottom 0.03 0.16 0.05 0. l4 0. 07 0.09 Viscosity at 100 F.,

SUS 292.4 326.3 291.2 321.8 270.9 309.1 Viscosity (corrected for Evaporation 313.6 311.0 304.3 Viscosity Increase,

percent 4.05 3.47 1.58

EXAMPLE III A Mid-Continent neutral lubricating oil like that used in the foregoing examples was inhibited 1 against oxidation with varying amounts of the sulfenamide prepared from tertiary butyl mercaptan and piperidinef The results are shown in Table IV. From a comparison of the properties of the'blends with those of the blank after heating in air at 350 F. for twenty-four hours it will be seen that the inhibitor displayed substantially its full etfectiveness when 0.10 per cent 7 was added'and that increase up to 2.00 per cent brought about substantially no improvement.

2. An improved lubricant comprising a major proportion of a lubricating oil and as an oxida- TABLI IV N-t-butylsulfenylpiperidine as inhibitor b0 utrali N 11th Pel Cent oi Eva ration Bayboit n asidue ution insoluble mummfgss Unmm'l Ramsbottom Number Per Cent Seconds Heated at 350" r 000 3.86 821.4 0.15 0.40 0.00 Unbniefl 200. a 0.00 000 003 Heated at 050 1' o. 10 3.20 013.0 0.20 0. 14 0.02 U L I 200.4 000 011 Heated at350F 025 s00 311.5 0.00 0.20 0.01

L 281. 1 0.00 0. 10 Heated at 350 F 0.50 3.44 318.0 00a 03a 00a Unhnnmd 282. 8 0. 04 0. l0 Heated at 050 F 1.00 4.00 0112 004 024 003 Unheate 276. 5 0. 01 0. 17 Heated at 050 F... a 00 a 82 an. a 0. 0e 0. 21 0. 0s Unheated 26L 9 0. 07 0. 22

EXAMPLE 1V tion inhibitor therefor a tertiary alkyl sulfen- A Mid-Continent neutral lubricating 011 like that used in the previous examples was inhibited with varying amounts of the sulfenamide prepared from diamylamine and tertiary butyl mercaptan. The results of tests on the resulting blends are set forth in Table V.

Teen: V

amide, said sulfenamide being present in an amount ranging from 0.01 to 5 per cent by weight 25 of said 011.

3. An improved lubricant comprising a major proportion of a lubricating oil and as an oxida- MN-diam i-f-but l sulfenamide as inhibitor is. 100 F Per Cent of Eva ration Baybolt 533 3, 2 25: gggggfi Inhibit 3 Universal Ramsbottom Number Per Cent Seconds Heated 8|; 350 F 0. 00 3- 4 324. 0 V 0- 14 0e 33 0. M U i' 290.3 0.02 0.0) Heated at 350 F *0. 3. 8 320. 5 0- 0- 35 0. 06 Unheated 289. 4 0. 04 0. ll) Heated 8'; 350 F- 332 3 0- 22 0- 38 0. 06 Unheated 288. 6 0- 03 0. ill Hflllted at 350 F 0. 4- 3 329- 4 0- 24 0. 42 0.10 U 1 M8 0.0 0.) Heated at 350 F 1. 00 4. B 313. 5 0. 07 0. 24 0. 06 U i 281. l 0.05 0. 00 Heated at 350 F 2. 00 4. 8 313- 0 0- 07 0. 15 0. 01 Unhnnfnri 270.8 0.05 0.1

From Table V it will be noted that substantiall no further reduction in the viscosity of the oil occurred when an amount greater than 1.00

' per cent of the inhibitor was employed.

From the foregoing it will be apparent that use of the alkyl sulfenamides as lubricating oil additives is very advantageous. Among advantages effected by the present invention are that it rovides a cheap and effective method or reducing the oxidation tendency of lubricating oil, the additives used are free from objection since they form no undesirable products in the oil and are not corrosive and are not injurious to the engine, and they are readily prepared from cheap and readily available raw materials. A very important advantage is that by means of the present invention the oil is inhibited against oxidation more effectively than with the antioxidants now commercially available and at a fraction of the cost of using present antioxidants. Numerous other advantages of our invention will be apparent to those skilled in the art.

We claim:

1. An improved lubricant comprising a major proportion of a lubricating oil and as an oxidation inhibitor therefor an unsubstituted alkyl sulfenamide, said sulfenamide being present in an amount ranging from 0.01 to 5 per cent by weight of said oil.

tion inhibitor therefor an unsubstituted aikyl sulfenamide having the general formula H: HI

Ha Ha wherein R is an alkyl group, said sulienamide being present in an amount ranging from 0.01 to 5 per cent by weight'oi' said oil.

4. An improved lubricant comprising a major I proportion of a lubricating oil and as an oxidation inhibitor therefor a tertiary alkyl sulien- 6. An improved lubricant comprising a major proportion of a lubricating oil and as an oxidation inhibitor therefor an unsubstituted alkyl sulfenamide having the general formula.

HI Ha C-O wherein R is an alkyl group, said sulfenamide being present in an amount ranging from 0.01 to 5 per cent by weight of said oil.

7. An improved lubricant comprising a major proportion of a lubricating oil and as an oxidation inhibitor therefor a tertiary alkyl sulfenamide having the general formula wherein R is a tertiary alkyl group, said sulfenamide being present in an amount ranging from 0.01 to 5 per cent by weight of said oil.

8. An improved lubricant comprising a major proportion of a lubricating oil and as an oxidation inhibitor therefor N-t-butylsulfenylpiperidine, said sulfenamide being present in an amount wherein R1 is selected from the group consisting of unsubstituted alkyl groups and R2 and Rs are selected from the group consisting ofhydrogen, substituted and unsubstituted alkyl, aralkyl, aromatic or cycloalkyl groups and wherein R2 and R: may be the same or different and wherein R2 and R3 may be part of a cyclic structure, said sulfenamide being present in an amount ranging from 0.01 to 5 per cent by weight of said oil.

10. An improved lubricant comprising a major proportion of a lubricating oil and as an odixation inhibitor therefor N-phenyl-N-methyl-tbutyl sulfenamide, said sulfenamide being present in an amount ranging from 0.01 to 5 per cent by weight of said oil.

11. A lubricant in accordance with claim 5 wherein said sulfenamide is employed in an amount substantially equal to 0.25 weight per cent based on the weight of said oil.

CHESTER M. HIMEL. GRANT C. BAILEY.

REFERENCES CITED I The following references are of record in the ranging from 0.01 to 5 per cent by weight of said fil of this patent:

oil.

9. An improved lubricant comprising a major proportion of a lubricating oil and as an oxidation inhibitor therefor an unsubstituted alkyl sulfenamide having the general formula UNITED STATES PATENTS Rosen et a1 Dec. 15, 1942 

